My screen size is magnified? How to reset back to its normal screen size

Double-tap with three fingers.

I tried everythg but to no avail.

You can't have tried everything, otherwise you would've found the solution:

http://support.apple.com/kb/HT3577

The "Zoom" accessibility feature is turned on. Double-tap using three fingers to un-zoom, and then go to Settings -> General -> Accessibility -> Zoom and tap the Zoom On/Off switch.

If you have trouble with that. connect to iTunes and click the "Configure Universal Access" button in the Summary pane and turn off Zoom there.

This can be found in the manual:

http://manuals.info.apple.com/enUS/iPhone_UserGuide.pdf

Brilliant. Thank you ++
I'm not the original poster - just a grateful searcher with the same problem.

Good to know that search still works, and someone actually uses it. Thanks for the info.